Method for producing a rotor

ABSTRACT

In a method for producing a rotor including a leak prevention hole formed in a rotor core to prevent leakage of magnetic flux from a permanent magnet; an outer-circumferential-side dovetail groove formed in an outer-circumferential-side inner wall of the leak prevention hole, an inner-circumferential-side dovetail groove formed, opposite the outer-circumferential-side dovetail groove, in an inner-circumferential-side inner wall of the leak prevention hole; and a non-magnetic bridge having both end portions engageable with the dovetail grooves, an external force is applied to bring the outer-circumferential-side inner wall close to the inner-circumferential-side inner wall, the non-magnetic bridge is inserted in the dovetail grooves while keeping the rotor core in an elastically deformed state, and, after inserting, the external force is released.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2014-225339, filed Nov. 5,2014, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a rotorincluding a rotor core provided with a central hole and a hole formagnet (a magnet hole) formed in an outer circumferential portion, apermanent magnet mounted in the magnet hole, and a rotor shaftpress-fitted in the central hole.

Related Art

Motors for hybrid vehicles and others are severely demanded for sizereduction more than regular motors. Downsized motors tend to rise intemperature. Such a motor is more likely to cause a decrease in magneticflux of a magnet at high temperature than in conventional motors. Toprevent this decrease in magnetic flux density at high temperature,magnet material would be mixed with rare metal such as dysprosium. Therare metal is however expensive and hence leads to cost increase.

In order to reduce the amount of magnet material) and also decrease theamount of electric current to a stator to thereby reduce the amount ofheat generation of a motor, it is an effective method to prevent leakageof magnetic flux in the rotor core and reduce consumption current of themotor. In Patent Document 1, accordingly, a rotor core is split intoouter circumferential pieces in which magnetic flux will flow and aninner circumferential piece, which are coupled by non-magnetic bridges,to prevent the magnetic flux from leaking to the inner circumferentialpiece. Patent Document 2 also discloses that a bridge for reinforcingthe strength of a magnet insertion hole is made of non-magnetic materialto prevent magnetic flux leakage.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2010-193660

Patent Document 2: JP-A-2009-201269

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the conventional rotors would cause the following problems. InPatent Document 1, specifically, the rotor core is formed of theseparate outer and inner circumferential pieces, which are fixed to eachother with the non-magnetic bridges. Thus, since variations in assemblyaccuracy reflect in an outer diameter of the rotor core, this wouldcause a problem with difficulty in reducing a gap or clearance between astator and a rotor. To reduce the amount of current to be supplied tothe stator, the clearance between the stator and the rotor should bereduced, but such a reduction would be irrealizable.

Further, if the outer diameter of the rotor changes, not only the riskof interference with the stator, but also motor torque and motor lossvary disadvantageously.

In Patent Document 2, the non-magnetic bridges couple an outercircumferential portion located more outside than the magnet insertionholes to an inner circumferential portion located more inside than themagnet insertion holes to prevent the outer circumferential portion fromexpanding outward by a centrifugal force. For this purpose, both endportions of each non-magnetic bridge are press-fitted in dovetailgrooves of the outer and inner circumferential portions. In thispress-fitting process, the non-magnetic bridge would rub against theinner wall surfaces of the dovetail grooves, which may cause generationof fine or minute friction dust. Such friction dust may enter variousplaces in the motor when mounted and driven in a hybrid vehicle,resulting in damage thereto.

In a case where a non-magnetic bridge is inserted with a clearance intoa pair of dovetail grooves, the outer circumferential portion of therotor core may be deformed by a centrifugal force. The clearance betweenthe outer periphery of a rotor and a stator is originally small in orderto reduce the amount of current to be supplied to the stator. Thus, ifthe outer circumferential portion of the rotor core is even slightlydeformed, the clearance between the rotor and the stator is relativelygreatly changed, which may affect the rotation of the rotor.

The present invention has been made to solve the above problems and hasa purpose to provide a method for producing a rotor, including a step ofmounting both end portions of a non-magnetic bridge in a pair ofdovetail grooves without producing fine friction dust due to rubbing.

Means of Solving the Problems

To achieve the above purpose, one aspect of the invention provides amethod for producing a rotor including a rotor core provided with acentral hole and a magnet hole formed in an outer circumferentialportion, a permanent magnet mounted in the magnet hole, and a rotorshaft press-fit in the central hole, wherein the rotor includes: amagnetic flux leakage prevention hole formed in the rotor core toprevent leakage of magnetic flux from the permanent magnet; anouter-circumferential-side dovetail groove formed in anouter-circumferential-side inner wall defining the magnetic flux leakageprevention hole on an outer circumferential side and aninner-circumferential-side dovetail groove formed, opposite theouter-circumferential-side dovetail groove, in aninner-circumferential-side inner wall defining the magnetic flux leakageprevention hole on an inner circumferential side; and a non-magneticbridge having both end portions being wide-width portions individuallyengageable with the outer-circumferential-side dovetail groove and theinner-circumferential-side dovetail groove, and wherein the methodincludes: applying an external force to the rotor core to cause elasticdeformation of the rotor core so that the outer-circumferential-sideinner wall of the magnetic flux leakage prevention hole comes close tothe inner-circumferential-side inner wall; inserting the both endportions of the non-magnetic bridge one in each of theouter-circumferential-side dovetail groove and theinner-circumferential-side dovetail groove while keeping the rotor corein an elastically deformed state; and releasing the external force afterinserting the non-magnetic bridge.

According to the foregoing configuration, while the non-magnetic bridgeis being inserted in the pair of dovetail grooves, there are clearancesbetween the non-magnetic bridge and the inner wall of theouter-circumferential-side dovetail groove and between the non-magneticbridge and the inner wall of the inner-circumferential-side dovetailgroove. This can avoid generation of fine friction dust. Since the leakmagnetic flux can be reduced, furthermore, the amount of magnet materialcan be decreased, thus resulting in reduced cost of a motor.

Moreover, when the external force is released after insertion of thenon-magnetic bridge in the pair of dovetail grooves, the non-magneticbridge and the inner wall surfaces of the pair of dovetail groovescontact with each other at a constant force. This makes it possible toprevent the outer circumferential portion of the rotor core from gettingdeformed outward in a radial direction when the centrifugal force actson the rotor, thereby enabling continuously keeping the clearanceconstant between the rotor and the stator. Thus, the rotation of therotor is less likely to be affected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration view of a rotor in an embodiment of theinvention;

FIG. 2 is a partial enlarged view of FIG. 1;

FIG. 3 is a view of the rotor of FIG. 2, in which a permanent magnet isunmounted;

FIG. 4 is a view showing a state in which a pressing force is applied;

FIG. 5 is a partial enlarged view of FIG. 4, showing a state ofinserting a non-magnetic bridge;

FIG. 6 is a view showing a state in which the pressing force isreleased;

FIG. 7 is a partial enlarged view of FIG. 6;

FIG. 8 is a view showing a step of pressing a rotor core;

FIG. 9 is a graph showing data on variation in outer diameter; and

FIG. 10 is a view showing a chamfered state of non-magnetic bridges.

DESCRIPTION OF EMBODIMENTS

A detailed description of a preferred embodiment of a method forproducing a rotor core will now be given referring to the accompanyingdrawings. FIG. 1 is a configuration view of a rotor 1. FIG. 2 is apartial enlarged view of the rotor 1. FIG. 3 is a view of the rotor 1 ofFIG. 2, in which permanent magnets 3, 4, and 5 and non-magnetic bridges6 are unmounted.

A rotor core 2 is made of stacked or laminated several hundred thinplates produced by way of punching a magnetic steel plate having athickness 0.1 to 0.3 mm by a press. Each thin plate is formed with aplurality of dowels in half-cut shape not shown so that the thin platesare stacked one on another with a projection of each dowel being fittedin a recess of each adjacent dowel. Accordingly, first magnet holes 12,second magnet holes 13, third magnet holes 14, and others are formedwith respective inner wall surfaces accurately aligned.

In a central hole 11 of the rotor core 2, a rotor shaft 10 is fitted. Inan outer circumferential portion of the rotor core 2, there are formedthe first magnet holes 12 (12A to 12H) in eight positionscircumferentially spaced at equal angular intervals (45 degrees),serving as holes for holding circumferential-direction magnets. In thoseholes 12, the permanent magnets 3 (3A to 3H) are individually mounted.Magnetic poles of each permanent magnet 3 are defined, for example, sothat the north pole is located on an outer circumferential side and thesouth pole is located on an inner circumferential side.

On both sides of each first magnet hole 12 in the circumferentialdirection of the rotor core 2, a pair of second magnet hole 13 and thirdmagnet hole 14 serving as holes for holding radial-direction magnets areformed to extend in a radial direction (a nearly radial direction) ofthe rotor core 2. Furthermore, a core outer-circumferential connectingportion 16 is formed on a core outer circumferential side of each secondmagnet hole 13. A core outer-circumferential connecting portion 17 isformed on a core outer circumferential side of each third magnet hole14.

In the second magnet holes 13, the permanent magnets 4 are individuallymounted. The permanent magnets 4 are each oriented so that one surfaceclose to the corresponding permanent magnet 3 is the north pole and anopposite surface is the south pole. In the third magnet holes 14, thepermanent magnets 5 are individually mounted. The permanent magnets 5are each oriented so that one surface close to the correspondingpermanent magnet 3 is the north pole and an opposite surface is thesouth pole.

Between each pair of the second magnet holes 13 and the third magnetholes 14, there is formed a leak prevention hole 15 to prevent leakageof magnetic flux from the permanent magnets 3, 4, and 5. The secondmagnet hole 13 and the third magnet hole 14 are continuous as a holethrough the leak prevention hole 15.

Further, a pair of leak prevention holes 18 and 19 are formed on bothsides of each first magnet hole 12 in the circumferential direction ofthe rotor core 2 to prevent leakage of magnetic flux. This is to havethe magnetic flux of the permanent magnet 3 concentrate between the leakprevention holes 18 and 19 and the outer periphery of the rotor core 32when teeth of a stator come close to the permanent magnet 3.

An inner wall (“outer-circumferential-side inner wall”) 15 a of the leakprevention hole 15 on the outer circumferential side is formed witheight outer-circumferential-side dovetail grooves 20 (20 a to 20 h). Aninner wall (“inner-circumferential-side inner wall”) 15 b of the leakprevention hole 15 on the inner circumferential side is formed withinner-circumferential-side dovetail grooves 21 (21 a to 21 h) oppositethe outer-circumferential-side dovetail grooves 20 a to 20 h. In eachopposite pair of the outer-circumferential-side dovetail grooves 20 a to20 h and the inner-circumferential-side dovetail grooves 21 a to 21 hwhich are arranged respectively opposite to each other, one end portion61 (61 a to 61 h) of the corresponding non-magnetic bridge 6 (6 a to 6h) and the other end portion 62 (62 a to 62 h) (see FIG. 5) areinserted.

In FIG. 1, in each of the first magnet holes 12 (12A to 12H), the spacenot occupied with the permanent magnet 3 (3A to 3H) is filled with resinby molding. In each of the second magnet holes 13, the space notoccupied with the permanent magnet 4 (4A to 4H) is filled with resin bymolding. In each of the third magnet holes 14, similarly, the space notoccupied with the permanent magnet 5 (5A to 5H) is filled with resin bymolding.

As shown in FIG. 5, each of the non-magnetic bridges 6 (6 a to 6 h)includes an end portion 61 (61 a to 61 h) which is an expanded, orwide-width, portion formed at one end in a length direction (an up-downdirection in FIG. 5) and an end portion 62 (62 a to 62 h) which is anexpanded, or wide-width, portion formed at the other end. Each endportion 61 is formed with a curved surface 611 (611 a to 611 h) on aside close to the opposite end portion 62. Each end portion 62 is formedwith a curved surface 621 (621 a to 621 h) on a side close to theopposite end portion 61.

Each of the non-magnetic bridges 6 is an I-shaped member having a heightequal to the thickness of the rotor core 2 in a direction perpendicularto the drawing sheet of FIG. 1 (i.e., in an axial direction of the rotorcore 2), in which the cross sectional shape shown in FIG. 5 iscontinuous throughout the height. The end portions 61 and 62 of eachI-shaped non-magnetic bridge 6 are each formed with a chamfer 63 (63 a,63 b) over a whole circumference at one of both end faces in a heightdirection as shown in FIG. 10. This chamfer 63 is formed in only the oneend face of each non-magnetic bridge 6, but it is not formed in theother end face.

Specifically, the non-magnetic bridge 6 a is inserted upward from belowinto the rotor core 2 in FIG. 10, while the non-magnetic bridge 6 b isinserted downward from above into the rotor core 2 so that respectiveone end faces formed with the chamfers 63 enter first into the rotorcore 2. In the present embodiment, specifically, eight non-magneticbridges 6 a to 6 h are inserted into the rotor core 2 so that thenon-magnetic bridges 6 a, 6 c, 6 e, and 6 g are inserted upward frombelow, while the non-magnetic bridges 6 b, 6 d, 6 f, and 6 h areinserted downward from above.

In the present embodiment, the length of each chamfer 63 from the endface (i.e., the length in an up-down direction in FIG. 10) is 0.3 mm to0.5 mm, which corresponds to the thickness of one or two layers of thestacked steel plates constituting the rotor core 2. Thus, the steelplate or plates located in a position corresponding to the chamfer 63does not contact the non-magnetic bridge 6 and are in a free state. Inthe present embodiment, however, the non-magnetic bridges 6 a to 6 h arealternately inserted in opposite directions into the rotor core 2.Accordingly, even a steel plate located at the end face of the rotorcore 2 is pressed and held by four non-magnetic bridges, so that thesteel plate at the end face is suppressed from being deformed outward ina radial direction of the rotor core 2 by the centrifugal force. In thepresent embodiment, each non-magnetic bridge 6 is designed in one piece,but may be made of laminated non-magnetic steel plates.

Next, a method for inserting the non-magnetic bridges 6 will beexplained, referring to the accompanying drawings. FIG. 8 shows a stateof the rotor core 2 in which the permanent magnets 3, 4, and 5 and thenon-magnetic bridges 6 are not yet mounted. In this state, eightcompression units 30A to 30H are each moved inward in the radialdirection of the rotor core 2 to press and compress the rotor core 2 ata predetermined pressing force F in eight places. A part thereof isshown in an enlarged view of FIG. 4. In the present embodiment, therotor core 2 is pressed in to a compressed state simultaneously in eightplaces. As an alternative is to press the rotor core 2 into a compressedstate in opposite places in a diametrical direction of the rotor core 2,for example, in only two places by the units 30A and 30E.

As shown in FIG. 4, the pressing force F is applied along a center lineof the first magnet hole 12 of the rotor core 2. The first magnet hole12, the second magnet hole 13, the third magnet hole 14, and the leakprevention hole 15 are configured line-symmetrical with respect to thecenter line of the first magnet hole 12. This allows the coreouter-circumferential connecting portions 16 and 17 to be uniformlyelastically deformed by the pressing force F. This causes theouter-circumferential-side inner wall 15 a of the leak prevention hole15 to come close to the inner-circumferential-side inner wall 15 b whilekeeping their parallel relationship, so that theouter-circumferential-side dovetail grooves 20 a to 20 h also come closeto the inner-circumferential-side dovetail grooves 21 a to 21 hrespectively along each center line.

In this state, the eight non-magnetic bridges 6 a to 6 h aresimultaneously inserted into the rotor core 2. In other words, the fournon-magnetic bridges 6 a, 6 c, 6 e, and 6 g are inserted from back tofront of the drawing sheet of FIG. 4, while the four non-magneticbridges 6 b, 6 d, 6 f, and 6 h are inserted from front to back of thedrawing sheet.

At that time, the end portions 61 a to 61 h of the non-magnetic bridges6 are respectively inserted in the outer-circumferential-side dovetailgrooves 20 a to 20 h of the rotor core 2 and simultaneously the endportions 62 a to 62 h are respectively inserted in theinner-circumferential-side dovetail grooves 21 a to 21 h. This insertingstate (also an inserted state) of only one portion is shown in anenlarged view in FIG. 5.

As shown in FIG. 5, the pressing force F brings theouter-circumferential-side inner wall 15 a of the leak prevention hole15 close to the inner-circumferential-side inner wall 15 b while keepingtheir parallel relationship. Thus, the curved surface 611 formed in theone end portion 61 of the non-magnetic bridge 6, on the side close tothe other end portion 62, keeps a predetermined clearance with respectto a curved surface 201 (201 a to 201 h) formed near an opening of theouter-circumferential-side dovetail groove 20. Simultaneously, thecurved surface 621 formed in the other end portion 62 of thenon-magnetic bridge 6, on the side close to the one end portion 61,keeps a predetermined clearance with respect to a curved surface 211(211 a to 211 h) formed near an opening of theouter-circumferential-side dovetail groove 21.

Since both the end portions 61 and 62 of each non-magnetic bridge 6 areinserted respectively in the outer-circumferential-side dovetail groove20 and the inner-circumferential-side dovetail groove 21 while keepingthe state of FIG. 5, the whole outer periphery of the end portion 61remains spaced with the predetermined clearance from the inner wallsurface of the outer-circumferential-side dovetail groove 20 andsimultaneously the whole outer periphery of the end portion 62 remainsspaced with the predetermined clearance from the inner wall surface ofthe inner-circumferential-side dovetail groove 21. Thus, any finefriction dust will not be generated.

Subsequently, as shown in FIG. 6, the pressing force F applied to therotor core 2 is released. Specifically, after insertion of thenon-magnetic bridges 6, the compression units 30A to 30H are movedoutward in the radial direction of the rotor core 2, thereby releasing,or removing, the external force (the pressing force F) from the rotorcore 2. Accordingly, the curved surfaces 611 a to 611 h of the endportions 61 a to 61 h of the non-magnetic bridges 6 a to 6 h and thecurved surfaces 201 a to 201 h which are inner wall surfaces of theouter-circumferential-side dovetail grooves 20 a to 20 h are causedrespectively to contact with each other at a constant force. Further,the curved surfaces 621 a to 621 h of the end portions 62 a to 62 h ofthe non-magnetic bridges 6 a to 6 h and the curved surfaces 211 a to 211h which are inner wall surfaces of the inner-circumferential-sidedovetail grooves 21 a to 21 h are caused respectively to contact witheach other at a constant force. Of them, a part M in FIG. 6 is shown inan enlarged view in FIG. 7.

Accordingly, when the centrifugal force acts on the rotor 1, the outercircumferential portion of the rotor core 2 will not be deformedradially outward, so that the clearance between the rotor 1 and thestator can be kept continuously constant. The rotation of the rotor 1 isthus not affected.

On the other hand, it is conceivable to adopt clearance-fit for looseengagement in order to avoid the generation of fine friction dust causedby press-fit of the non-magnetic bridges 6. In this case, however, thefollowing problems may come about.

FIG. 9 is a graph showing a relationship between the number of motorrotations and the variation in outer diameter of the rotor core 2. Theouter diameter of the rotor core 2 in the present embodiment is 200 mmto 300 mm. A lateral axis of the graph represents the number ofrotations of a motor (a rotor), which is expressed in units of 1000 rpm.A vertical axis of the graph represents the variation in outer diameterof the rotor core 2 in units of mm.

In FIG. 9, N1 indicates a result of a rotor core realized by theclearance-fit, in which there are large or small variations in clearancebetween the both end portions of each non-magnetic bridge and thecorresponding dovetail groove inner walls. N2 indicates a result of therotor core 2 in the present embodiment. In the rotor core 2, all thecurved surfaces 611 and 621 of the both end portions 61 and 62 of thenon-magnetic bridges 6 are in continuously contact with the curvedsurfaces 201 and 211 of the dovetail grooves 20 and 21.

When the number of rotor rotations reaches a value half of the regularnumber of rotations, N1 indicates variations in the outer diameterchanging in the order of 0.01 mm, whereas N2 indicates almost novariation, or nearly zero. This reveals that the outer diameter of therotor core 2 in the present embodiment hardly changes even if the numberof rotor rotations increases.

In FIG. 2, magnetic flux flows G of the permanent magnets 4 and 5 areindicated with arrows. The magnetic flux flows G are considered to alsopass nearby the end portions 61 a to 61 h of the correspondingnon-magnetic bridge 6.

In a case where a single non-magnetic bridge 6 is provided for each leakprevention hole 15, the end portion 61 could be formed as a wide-widthportion having a large size (cross sectional area) from necessity forstrength. Such a large end portion may block or interfere with themagnetic flux flows G and cause deterioration in magnetic flux density.The present embodiment employs eight non-magnetic bridges 6 a to 6 h forsharing the burden of required strength, so that respective end portions61 a to 61 h have a smaller size (cross sectional area) than in the caseof the single non-magnetic bridge 6, thereby ensuring a large crosssection of the region of the rotor core 2 through which magnetic fluxeswill pass, thus leading to less interference with the magnetic fluxflows G.

(1) According to the rotor producing method of the present embodiment,as described in detail above, in the method for producing the rotor 1including the rotor core 2 provided with the central hole 11 and thefirst to third magnet holes 12 to 14 formed in the outer circumferentialportion, the permanent magnets 3 to 5 respectively mounted in the firstto third magnet holes 12 to 14, and the rotor shaft 10 press-fitted inthe central hole 11, the rotor 1 includes the leak prevention holes 15formed in the rotor core 2 to prevent leakage of magnetic flux from thepermanent magnets 3 to 5, the outer-circumferential-side dovetailgrooves 20 formed in the inner wall 15 a of each leak prevention hole15, the inner-circumferential-side dovetail grooves 21 formed, oppositethe outer-circumferential-side dovetail grooves 20, in theinner-circumferential-side inner wall 15 b of each leak prevention hole15, and the non-magnetic bridges 6 each having the both end portions 61and 62 respectively engageable with the outer-circumferential-sidedovetail grooves 20 and the inner-circumferential-side dovetail grooves21. The method includes applying the external force (the pressing forceF) to the rotor core 2 to cause elastic deformation of the rotor core 2so that the outer-circumferential-side inner walls 15 a of the leakprevention holes 15 come close to the correspondinginner-circumferential-side inner walls 15 b, inserting the both endportions 61 and 62 of the non-magnetic bridges 6 respectively in theouter-circumferential-side dovetail grooves 20 and theinner-circumferential-side dovetail grooves 21 while keeping the rotorcore 2 in an elastically deformed state, and, after inserting, thenreleasing the external force from the rotor core 2. Accordingly, whenthe non-magnetic bridges 6 are being inserted in the corresponding pairsof the dovetail grooves 20 and 21, there are clearances between eachnon-magnetic bridge 6 and each inner wall surface of theouter-circumferential-side dovetail grooves 20 and theinner-circumferential-side dovetail grooves 21. This can avoidgeneration of fine friction dust. Since the leak magnetic flux can bereduced, furthermore, the amount of magnet material can be reduced, thusresulting in reduced cost of a motor.

When the external force is released after insertion of the non-magneticbridges in the dovetail grooves 20 and 21, the non-magnetic bridges 6and the inner wall surfaces of the corresponding pairs of the dovetailgrooves 20 and 21 contact with each other at a constant force. Thismakes it possible to prevent the outer circumferential portion of therotor core 2 from getting deformed radially outward when the centrifugalforce acts on the rotor 1, thereby enabling continuously keeping theclearance constant between the rotor 1 and the stator. Thus, therotation of the rotor 1 is less likely to be affected.

(2) In the rotor producing method described in (1), the holes formagnets (the magnet holes) include the first magnet holes 12 formed toextend in a circumferential direction of the rotor core 2, the secondmagnet holes 13 and the third magnet holes 14 formed on both sides ofeach magnet hole 12 in the circumferential direction, each of the holes13 and 14 extending in the radial direction of the rotor core 2. Therotor core 2 is formed with the core outer-circumferential connectingportions 16 and 17 on the core outer circumferential sides of the secondmagnet holes 13 and the third magnet holes 14. The elastic deformationis caused in the core outer-circumferential connecting portions 16 and17. Specifically, when the external force is applied to the rotor core2, the pair of core outer-circumferential connecting portions 16 and 17are elastically deformed. This elastic deformation can thus besufficiently obtained by a relatively small force. Also, the coreouter-circumferential connecting portions 16 and 17 are deformed so thatthe outer-circumferential-side inner wall 15 a of each leak preventionhole 15 is kept in parallel to the inner-circumferential-side inner wall15 b. Consequently, even small elastic deformation allows the clearanceto be uniformly created between the non-magnetic bridges 6 and the innerwall surfaces of the corresponding pairs of the dovetail grooves 20 and21. In particular, in a case of using a plurality of the non-magneticbridges 6, the clearance can be uniformly formed for each of thenon-magnetic bridges 6 a to 6 h. This can facilitate insertion of theplurality of the non-magnetic bridges 6 a to 6 h without contacting withthe inner wall surfaces of the dovetail grooves 20 and 21.

(3) In the rotor producing method described in (1) or (2), thenon-magnetic bridges 6 include two or more non-magnetic bridges 6 eachincluding the both end portions 61 and 62 each formed as the wide-widthportion having a small size (cross sectional area) enough to ensure alarge cross-sectional area of the rotor core 2 through which magneticflux of the permanent magnets 3, 4, and 5 will pass. Thus, the endportions 61 and 62 of each non-magnetic bridge 6 can be reduced in sizeas compared with the conventional case. Accordingly, when each leakprevention hole 15 is formed with the necessary area, thecross-sectional area of the end portions 61 and 62 of each non-magneticbridge 6 which may interfere with the cross-sectional area of the rotarycore 2 through which the magnetic flux of the permanent magnets 3, 4,and 5 will pass can be reduced. Consequently, this can ensure a largecross sectional area through which the magnetic flux of the permanentmagnets 3, 4, and 5 will pass.

The present invention may be embodied in other specific forms withoutdeparting from the essential characteristics thereof. For instance, thepresent embodiment uses eight non-magnetic bridges 6, but may use two,four, six, or ten non-magnetic bridges.

INDUSTRIAL APPLICABILITY

The present invention is utilizable as a method for producing a rotorfor a motor to be used in a hybrid vehicle.

REFERENCE SIGNS LIST

1 Rotor

2 Rotor core

3, 4, 5 Permanent magnet

6 Non-magnetic bridge

10 Rotor shaft

12 First magnet hole

13 Second magnet hole

14 Third magnet hole

15 Leak prevention hole

16, 17 Core outer-circumferential connecting portion

20 Outer-circumferential-side dovetail groove

21 Inner-circumferential-side dovetail groove

What is claimed is:
 1. A method for producing a rotor including a rotorcore provided with a central hole and a magnet hole formed in an outercircumferential portion, a permanent magnet mounted in the magnet hole,and a rotor shaft press-fit in the central hole, wherein the rotorincludes: a magnetic flux leakage prevention hole formed in the rotorcore to prevent leakage of magnetic flux from the permanent magnet; anouter-circumferential-side dovetail groove formed in anouter-circumferential-side inner wall defining the magnetic flux leakageprevention hole on an outer circumferential side and aninner-circumferential-side dovetail groove formed, opposite theouter-circumferential-side dovetail groove, in aninner-circumferential-side inner wall defining the magnetic flux leakageprevention hole on an inner circumferential side; and a non-magneticbridge having both end portions being wide-width portions individuallyengageable with the outer-circumferential-side dovetail groove and theinner-circumferential-side dovetail groove, and wherein the methodincludes: applying an external force to the rotor core to cause elasticdeformation of the rotor core so that the outer-circumferential-sideinner wall of the magnetic flux leakage prevention hole comes close tothe inner-circumferential-side inner wall; inserting the both endportions of the non-magnetic bridge one in each of theouter-circumferential-side dovetail groove and theinner-circumferential-side dovetail groove while keeping the rotor corein an elastically deformed state; and releasing the external force afterinserting the non-magnetic bridge.
 2. The method for producing a rotoraccording to claim 1, wherein the magnet hole includes acircumferential-direction magnet hole formed to extend in acircumferential direction of the rotor core and a pair ofradial-direction magnet holes formed on both side of thecircumferential-direction magnet hole in the circumferential direction,each of the radial-direction magnet holes extending in a radialdirection of the rotor core, wherein the rotor core includes a coreouter-circumferential connecting portion on a core outer circumferentialside of each of the pair of radial-direction magnet holes, and whereinthe elastic deformation is caused in the core outer-circumferentialconnecting portions.
 3. The method for producing a rotor according toclaim 1, wherein the non-magnetic bridge includes two or morenon-magnetic bridges each having both end portions each formed as awide-width portion having a small size to ensure a large cross-sectionalarea of the rotor core through which the magnetic flux of the permanentmagnet will pass.
 4. The method for producing a rotor according to claim2, wherein the non-magnetic bridge includes two or more non-magneticbridges each having both end portions each formed as a wide-widthportion having a small size to ensure a large cross-sectional area ofthe rotor core through which the magnetic flux of the permanent magnetwill pass.